Endoprosthesis devices, more generally referred to as stents, are known in the art for treating a wide range of medical conditions. Generally, an endoprosthesis consists of a cylindrical device that can be expanded from a smaller diameter configuration to a larger diameter configuration. The smaller diameter configuration facilitates advancing the endoprosthesis through an often convoluted lumen of a patient while the expanded diameter configuration presses against the walls of the patient's lumen, often to both anchor the prosthesis and restore the patency of the lumen.
Many endoprosthesis devices can be classified according to their method of expansion. Some devices are expanded by the exertion of an outwardly directed radial force on an inner surface of the endoprosthesis. For example, the endoprosthesis may be compressed or crimped over a deflated balloon of a balloon catheter. When the endoprosthesis is positioned at a desired target area, the balloon is inflated, expanding the endoprosthesis.
Other endoprosthesis devices are self-expanding and therefore recover to an expanded position after being compressed. For example, some self-expanding endoprosthesis devices are composed of a shape memory material such as Nitinol (Ni—Tl alloy). The shape memory material allows the device to be compressed within a delivery catheter, yet expand in diameter when released within the lumen of a patient, similar to a spring. For some applications, self-expanding endoprosthesis devices are thought to be superior to balloon expandable devices since self-expanding devices often require less elaborate delivery mechanisms (e.g., no inflatable balloons) and are often less likely to be damaged after deployment (e.g., by being crushed or otherwise permanently deformed). Examples of prior art shape memory device can be seen in U.S. Pat. No. 4,665,905 to Jervis and U.S. Pat. No. 4,925,445 to Sakamoto et al., the contents of which are hereby incorporated by reference.
However, delivery systems for self-expanding endoprosthesis devices are not without their drawbacks. For example, one common delivery system includes a catheter having a retractable sheath. The endoprosthesis device is preloaded onto a reduced diameter region on a distal end of the catheter. The retractable sheath is positioned over the device, preventing it from expanding in diameter. When a desired target location is reached by the device, the user retracts the outer sheath, releasing the self-expanding device. However, the self-expanding force can cause the device to spring laterally out of the sheath, sometimes missing the desired target area. Further, the device may tend to become imbedded within the wall of the sheath, resulting in damage to the device or the device becoming stuck. Additional delivery system details can be found in U.S. Pat. Nos. 4,580,568 and 4,732,152, the contents of which are hereby incorporated by reference.
Accordingly, there is a need for a self-expanding endoprosthesis delivery system which overcomes the disadvantages of the prior art.